To gain insight into the pathogenesis of oculomotor disease and strabismus, we are investigating the genetic basis of congenital eye movement disorders referred to as 'congenital cranial dysinnervation disorders' (CCDDs) and studying how these genetic defects perturb development of the oculomotor lower motor neuron system. The neuropathologic findings in Duane syndrome and CFEOM1 and the role of the CFEOM2 gene, PHOX2A (ARIX), in midbrain development support the hypothesis that these disorders result from aberrant development of motor neurons or axonal targeting of cranial nerves with secondary extraocular muscle dysinnervation. We propose that CFEOM and ptosis result from maldevelopment of oculomotor and trochlear nuclei and nerves, Duane syndrome (DS) results from maldevelopment of abducens motoneurons, and horizontal gaze palsy (HGP) results from maldevelopment of abducens motoneurons and interneurons. We have defined five CCDD genetic loci and identified PHOX2A and SALL4 as the genes mutated in CFEOM2 and Duane radial ray syndrome, respectively. We are in the process of positionally cloning the remaining CFEOM genes. In this grant, we seek funding to identify two genes mutated in Duane syndrome (DURS1 and DURS2) and a gene mutated in horizontal gaze palsy with progressive scoliosis (HGPPS). By identifying these genes that cause complex horizontal strabismus we will define the genetic basis of these disorders, develop a tool with which to study their molecular etiologies, and gain important insight into the pathogenesis of oculomotor disease and abducens nuclear and nerve development. We will address these Aims by (1) Identifying the HGPPS disease gene and analyzing pedigrees for disease-causing mutations. (2) Identifying the DURS2 disease gene and analyzing pedigrees for disease-causing mutations. (3) Defining a new DURS1 cytogenetic breakpoint and determining if mutations in candidate DURS1 genes cause DS. (4) Determining if mutations in the identified DS and HGPPS genes cause sporadic DS and/or more common forms of horizontal strabismus. And (5) Initiating structural and functional characterization of the horizontal CCDD genes and their protein products.